48 アンブリオフラン誘導体の環化反応制御(±)-バイユノールの全合成

概要

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A sweet principle of Phlomis betonicoides, baiyunoside (1a) reported by Tanaka, is a glycoside of 3-substituted furanoditerpene with labdane skeleton. During the series of our investigation dealing with a biomimetic olefin cyclization using mercury(III) triflate/N,N-dimethylaniline complex (2), we have examined the cyclization of some acyclic furano terpenoid, and observed that the cyclization of ambliofuran (3a) is mainly initiated from an internal double bond (Δ^<10>) to give 4 and 5, whereas the corresponding sulfone 3b affords terminal cyclization products 16, 17, and 18. The latter product 18 is a mixture of three isomeric olefins (Δ^<7,8>:Δ^<8,9>:Δ^<8,17>=9:4:3). Thus, the cyclization control of ambliofuran analog not only the initiation point but also the termination mode is essential in order to promote the selective total synthesis of (±)-baiyunol (1b), an aglycon of a sweet substance 1a. A furano ketone 3d is the best substrate to our purpose which gives Δ^<8,9> bicyclic product 28 in high yield. The resulting organomercuric ketone 28 is efficiently transformed to 1b, and which is identified with (+)-baiyunol derived from natural sweet glycoside. Glycosidation of (±)-baiyunol is currently undertaken.
天然有機化合物討論会の論文
1986-09-09